The present invention relates to a heat-stable crystalline form of a dye and a process for preparing the same.
A dye represented by the following formula (1) is known in the art as disclosed in Japanese Patent Laid-Open (KOKAI) No. 49-13479 (1974): ##STR2##
It is known that the dye represented by the formula (1) dyes a synthetic fiber, e.g., a polyethylene terephthalate fiber, navy blue.
In recent years, the rationalization of dyeing operation and energy-saving measures have advanced in the dyeing industry and various attempts have been made in order to reduce the bath ratio and, at the same time, to adopt dyeing methods, such as Obermaier dyeing, cheese dyeing, beam dyeing and jet dyeing, wherein a dye liquor is circulated with the substrate being held in a resting state, so that development of a dye having an excellent dispersion stability at a high temperature has been eagerly desired in the art for the purpose of preventing uneven dyeing caused by a filter effect in dyeing process.
When the dye represented by the formula (1) and produced by an ordinary method is used for dyeing at a high temperature, for example, at a temperature of 95.degree. C. or higher, dispersion of dye particles in a dye bath unfavorably becomes poor, so that it is difficult to obtain a dyed material having a uniform dyeing depth.
The present inventors have made extensive and intensive studies with a view to solving the above-described problem, which has led to the completion of the present invention.